USMLE Step 2 CK Content Blueprint: Real Weighting by System and Discipline
USMLE publishes real percentage ranges for exactly how much of Step 2 CK each system and discipline is worth — not a rumor, an official table in the content outline specifications (https://www.usmle.org/exam-resources/step-2-ck-materials/step-2-ck-content-outline-specifications). These ranges are explicitly stated as subject to change at any time, so treat this as current as of that source, not permanent.
By System/Discipline (Table 1): Nutrition 15–20%, Social Sciences (Legal/Ethical Issues & Professionalism/Systems-based Practice & Patient Safety) 10–15%, Renal & Urinary System & Reproductive Systems 7–13%, Cardiovascular System 6–12%, Musculoskeletal System/Skin & Subcutaneous Tissue 6–12%, Behavioral Health 5–10%, Blood & Lymphoreticular/Immune Systems 5–10%, Gastrointestinal System 5–10%, Nervous System & Special Senses 5–10%, Respiratory System 5–10%, Multisystem Processes & Disorders 4–8%, Endocrine System 3–7%, Pregnancy, Childbirth & the Puerperium 3–7%, Biostatistics & Epidemiology/Population Health/Interpretation of Medical Literature 3–5%, Human Development 2–4%.
By Clinical Science (Table 3): Medicine 55–65%, Pediatrics 17–27%, Obstetrics & Gynecology 10–20%, Psychiatry 10–15%, Surgery 5–15% — these five intentionally add up to well over 100%, since USMLE's own methodology allows a single item to be double-classified across more than one clinical science category.
Study takeaway: weight your own study time the way the blueprint does: Nutrition and the Social Sciences cluster (legal/ethical/systems-based practice/patient safety) each carry as much or more real exam weight as core organ systems like cardiovascular, so don't treat them as an afterthought behind the traditionally 'higher-yield-feeling' systems — and within Clinical Science, Medicine alone accounts for more than half the exam, by a wide margin over any other single category.